Equivalent Source Research Articles

Electromagnetic Time Reversal in the Near Field: Characterization of Transient Disturbances in Power Electronics

In the article, the electromagnetic time reversal technique (EMTR) is studied in the electromagnetic compatibility context. The main issue addressed by this approach is to deal with electromagnetic (EM) radiating source identification. This article is intended to provide a time-domain (TD) study of EMTR in the near field (NF) and prove its efficiency in characterizing transient disturbances in power electronics. The reconstruction of EM emissions is based on two stages. First, the modeling process relies on the use of TD analytical expressions. Second, signal processing is referring to the time reversal technique, which defines an inverse problem resolution. The method proposes to identify a set of equivalent dipoles. The validation is carried out experimentally using a TD measurement bench. The main purposes of this method is to extract the dipoles locations, moments, and orientation. The magnetic field maps calculated at each time step using obtained equivalent sources are compared with measured distributions. Adequate agreement is achieved, which confirms the efficiency of the proposed method. In addition, for validation purposes, the equivalent model is compared with that obtained by a frequency-domain (FD) method based on the standard genetic algorithms. Unlike FD, TD investigations allow characterizing transient disturbances in power electronic systems that emit strong EM interferences, by finding a sufficient equivalent model valid on a wide frequency band at once.

Large-Signal Stable Nonlinear Control of DC/DC Power Converter With Online Estimation of Uncertainties

The passivity-based control (PBC) is recognized as an effective energy shaping approach to guarantee the asymptotic stability of the whole system by using the passivity property. However, the model- and sensor-based characteristics limit its development and application. The combination of the PBC and online estimation technique can solve these problems. The purpose of this article is to propose a controller and an observer, which are designed simultaneously based on Hamiltonian framework and Lyapunov criterion. It leads to the system design without separation of the dynamics of the controller and the observer. The uncertainties in the model and parameters are considered as equivalent voltage and current sources. To reduce the number of sensors, input voltage, output current, and equivalent sources are estimated together. The steady-state error is eliminated by using this estimation technique. The exponential stability of the whole system (converter, controller, and observer) is proved by using a proper Lyapunov function. Simulation and experimental results from a 3-kW 270–350-V dc/dc boost converter with a constant power load (CPL) are performed to confirm the proposed control algorithm. Since the system parameter values may vary with temperature and the equilibrium point, the robustness of the proposed method is verified without and with parameters uncertainties.

Extended-resolution acoustic imaging of low-frequency wave sources by acoustic analogy-based tomography

Abstract

Magnetic switching of Kerker scattering in spherical microresonators

Abstract Magneto-optical materials have become a key tool in functional nanophotonics, mainly due to their ability to offer active tuning between two different operational states in subwavelength structures. In the long-wavelength limit, such states may be considered as the directional forward- and back-scattering operations, due to the interplay between magnetic and electric dipolar modes, which act as equivalent Huygens sources. In this work, on the basis of full-wave electrodynamic calculations based on a rigorous volume integral equation (VIE) method, we demonstrate the feasibility of obtaining magnetically-tunable directionality inversion in spherical microresonators (THz antennas) coated by magneto-optical materials. In particular, our analysis reveals that when a high-index dielectric is coated with a magneto-optical material, we can switch the back-scattering of the whole particle to forward-scattering simply by turning off/on an external magnetic field bias. The validity of our calculations is confirmed by reproducing the above two-state operation, predicted by the VIE, with full-wave finite-element commercial software. Our results are of interest for the design of state-of-the-art active metasurfaces and metalenses, as well as for functional nanophotonic structures, and scattering and nanoantennas engineering.

Basin modelling and bulk kinetics of heterogeneous organic-rich Nyalau Formation sediments of the Sarawak Basin, Malaysia

The investigation of the Nyalau Formation and its offshore equivalents (Cycles I and I) using 1D-basin modeling was carried to evaluate the timing and maturity aspects of their petroleum system. The Nyalau Formation and its offshore equivalents show a very remarkable source rock sequence for oil and gas in the Sarawak Basin. About twenty typical samples of the Nyalau Formation, with its maturity range beginning at immature to early-mature were evaluated, adopting bulk and quantitative pyrolysis procedures to reveal the kerogen characteristics and define the inherent optical properties of the organic matter and the effect it has on petroleum generation. Pyrolysis data identified two organic facies that indicate petroleum generation tendencies; Kerogen Type II/III having fairly high values of hydrogen index (HI) above 200 mg HC/g TOC whilst the kerogen Type III is comparatively with low HI values below 200 mg HC/g TOC. The aforementioned is reinforced with respect to distribution appertaining to energy activation a derivative of the bulk kinetic analysis. This study in a wide distribution of energy activation of kcal/mole to 69 kcal/mol which is unswervingly correlated heterogeneously to the organic matter. Also, the bulk kinetic analysis shows substantial variation in petroleum formation tract with regards to onset as well as the Nyalau's source rocks samples peak generation temperatures.At the temperatures between 121 and 131 °C petroleum generation for kerogen Type II/III commenced while at the temperatures of 134–145 °C for kerogen Type III. There is a variation of the peak generation temperatures (geological temperature maximum) in the range of 135–142 °C for Type II/III kerogens, whilst 153–167 °C for kerogen Type III. A notable transformation ratio of about 33% is reached as a result of these peak generation temperatures. The results were then integrated into the basin modelling, thereby predicting the timing, generation, and expulsion of hydrocarbons from the Nyalau equivalent source rocks in the offshore basin. This models suggests the onset of petroleum generation from Nyalau source rocks began in the Early Miocene (23-16 Ma), and the generation peaked at the Middle Miocene (18-12 Ma). The evolution and the expulsion of hydrocarbon as modeled indicate the timing of the expelled petroleum commenced in Pliocene and continued to present-day (5–0.0Ma). One dimensional basin models and bulk kinetics provide a quantitative way of predicting the timing, generation, and expulsion of hydrocarbon from Nyalau Formation within the Sarawak Basin.

A modeling method for equivalent source adopting volume structure technique in FDTD

The equivalent source is a widely used approach for simulating hybrid electromagnetic (EM) field-circuit problems. In this approach, three techniques, e.g., the wire, surface, and volume structure, can be employed for embedding lumped circuits into finite difference time-domain cells. However, the volume structure technique introduced in previous studies may result in incorrect answers when addressing problems consisting of electronic devices loaded onto conductor strip gaps. To fix this problem, an extra processing method is proposed. Based on the condition of consistent potential on the same tangent plane in the loading direction, this approach assigns the EM field on the grids occupied by the lumped circuit to obtain the equivalent source information. A numerical example is presented, the structure of which consists of a Schottky diode mounted across a microstrip gap. The results validate the feasibility of the proposed method.

Analytical Correlation Between Time and Frequency Domain Shielding Effectiveness of Metallic Enclosures With Apertures

Time domain shielding effectiveness (SE) of metallic enclosures with apertures against electromagnetic pulse excitation has been analytically estimated and correlated to the frequency domain characteristics. The method is based on the analysis of the transient process at the aperture and an equivalent magnetic current source, to derive the initial peak amplitude appearing at the very beginning of the coupled field waveforms. The equivalent circuit model is utilized to analytically describe the frequency domain SE data. Then, a simple correlation formula has been derived, which relates the peak value reduction of the E-field and H-field to the specified spectral data minus a specially defined factor. Especially, the correlation for the E-field is shown to link the spectral SE data near the fundamental resonant frequency of TE101 mode with the peak amplitudes in time domain. A series of numerical and experimental cases have been checked to confirm the applicability of the analytical formulas. Comparisons between the data and the analysis exhibit reasonable agreements.

Three-dimensional sound scattering from transversely symmetric surface waves in deep and shallow water using the equivalent source method.

This paper proposes a propagation model to calculate the three-dimensional (3-D) sound scattering from transversely symmetric sea surface waves in both deep and shallow water using the equivalent source method (ESM). The 3-D sound field is calculated by integrating an assembly of two-dimensional (2-D) transformed fields with different out-of-plane wavenumbers through a cosine transform. Each 2-D solution is calculated using the ESM incorporating a complex image method that can efficiently and accurately solve the 2-D water/seabed Green's function. The oscillatory cosine integral is accurately calculated using a segmented integral scheme requiring relatively few 2-D solutions, which can be further improved through the use of parallel computation. The model is validated by comparison with a 3-D Helmholtz-Kirchhoff method for deep water and a finite element method for a shallow water wedge with both a fluid and an elastic seabed. The model is as accurate as the finite element approach but more numerically efficient, which enables Monte Carlo simulations to be performed for random rough surfaces in order to study the scattering effects at a reasonable computational cost. Also, 3-D pulse propagation in the shallow water wedge is demonstrated to understand the out-of-plane scattering effects further.

Direct Solution of Scattering Problems Using Generalized Source Integral Equations

A class of inherently compressible integral equation formulations for problems of scattering by impenetrable objects, which makes use of generalized directional sources, is presented. The new formulation effectively reduces the problem's dimensionality and, thus, allows for efficient low-rank compression of moment matrices' off-diagonal blocks. When the formulation is used with a hierarchical matrix compression and factorization algorithm, a fast direct solver is obtained. The computational bottlenecks introduced by the proposed generalized formulation, in both the matrix-fill and matrix compression stages, are alleviated by using nonuniform sampling-based techniques. These techniques are described in detail for one choice of generalized sources, which use absorbing equivalent source shields, and can be extended to other shield types. The formulation's properties and limitations are studied and its enhanced compressibility is used for the development of a fast direct solver.

Efficient analysis of coated object using fast algorithm with surface impedance boundary condition

An effective solution method is proposed to analyze the electromagnetic scattering problem of coated targets, which is based on a novel form of multilevel matrix decomposition algorithm (NFMLMDA). It uses an efficient directional grouping scheme to subdivide the far-field domain, and then a novel distribution form of equivalent source is applied to reduce the matrix filling time and memory requirement. By using the grouping scheme, the far-field interaction domain can be divided into many cone structures. The matrix between the observation group and far-field group in the cone structure is low-rank, which meets the directional far-field requirement. Meanwhile, the impedance boundary condition (IBC) is applied to simplify the solution process and improve the accuracy of the approximate solution. The method of this paper is very suitable for the needs of various kinds of complex problems.

Exact extrapolation and immersive modelling with finite-difference injection

SUMMARY In numerical modelling of wave propagation, the finite-difference (FD) injection method enables the re-introduction of simulated wavefields in model subdomains with machine precision, enabling the efficient calculation of waveforms after localized model alterations. By rewriting the FD-injection method in terms of sets of equivalent sources, we show how the same principles can be applied to achieve on-the-fly wavefield extrapolation using Kirchhoff–Helmholtz (KH)-like integrals. The resulting extrapolation methods are numerically exact when used in conjunction with FD-computed Green’s functions. Since FD injection only relies on the linearity of the wave equation and compactness of FD stencils in space, the methods can be applied to both staggered and non-staggered discretizations with arbitrary-order spatial operators. Examples for both types of discretizations show how these extrapolators can be used to truncate models with exact absorbing or immersive boundary conditions. Such immersive modelling involves the evaluation of KH-type extrapolation and representation integrals in the same simulation, which include the long-range interactions missing from conventional FD injection.

An approach for indoor prediction of the pass-by noise of a vehicle based on the time-domain equivalent source method

An approach based on the time-domain equivalent source method (TESM) is developed for the indoor prediction of the pass-by noise of a vehicle in a small-scale semi-anechoic chamber. In the approach, a vehicle drives on a chassis dynamometer, and a number of microphones are distributed around the vehicle to measure the pressure radiated by the vehicle in the near field. Based on the idea of TESM, the sound sources generated by the vehicle are modeled by a series of time-domain equivalent sources, and the sound radiated from these sources to the microphones is depicted by the half-space Green’s function that takes the reflections from the rigid ground into account. To evaluate the pass-by noise, the strengths of equivalent sources are first solved by using the measured pressures as the input of TESM, and then the pressures on the target points specified by the ISO 362-3 Standard are reconstructed by the superposition of sound fields generated by the equivalent sources. Finally, the sound pressure level (SPL) of the pass-by noise can be calculated from the reconstructed pressures. In particular, the proper arrangement scheme for the equivalent sources is investigated in numerical simulations to ensure the prediction accuracy. Numerical and experimental results demonstrate that the proposed approach can effectively predict the SPL of the pass-by noise of a vehicle for both constant-speed and accelerated test conditions in a small-scale semi-anechoic chamber.

Modeling and experimental validation on temperature diffusion mechanism in high-speed bone milling

• High-speed bone milling heat is mainly caused by the friction effect between the bone chip and the cutter tooth. • Cutting edge temperature is determined by the equivalent static plane heat source. • The bone material temperature distribution is obtained according to the constant temperature moving heat source. • The thermal damage factors could be calculated based on the temperature diffusion mechanism model in bone milling. In orthopedic surgery, thermal damage of bone affects the accuracy of the prosthesis fixation and delays the postoperative recovery time. In order to avoid thermal damage in high-speed bone machining, it is necessary to establish an effective relationship among machining parameters, tool parameters, and temperature distribution of bone materials. Based on the characteristics of bone material and high-speed processing, this study proposes a novel temperature diffusion mechanism model (TDMM) in high-speed bone milling. According to the model, heat during high-speed bone milling is mainly generated by the friction effect between the bone chip and the cutter tooth. Then the cutting edge temperature of the milling cutter is determined by the equivalent static heat source, and cutting edge is regarded as a moving heat source with constant temperature. Under the action of the moving heat source, the bone material temperature distribution was determined. Moreover, the degree of thermal damage of bone materials under different machining and tool parameters was evaluated. Next, a high-speed bone milling experiment platform was established, in order to obtain accurate cutting edge temperature and bone material temperature. According to a large number of experimental measurements, the theoretical prediction temperature values of the cutting edge and bone materials were found to be within the reasonable error range of experimental measurements. The proposed model was proved to reasonably predict the temperature of the cutting edge and bone materials in high-speed bone milling. Experimental results indicate that the processing methods, tool diameter, cooling method, and cutting layer have a noteworthy impact on bone material distribution in bone milling. Spray cooling method can reduce the bone material temperature significantly. And the bone material temperature outside the cutting layer can be greatly lower than that in the cutting layer. This study also indicates that according to the TDMM, it is convenient for surgeons to select the appropriate machining parameters, and for engineers to optimize tool design.

A Novel Emission Test Method for Multiple Monopole Source Stirred Reverberation Chambers

This letter presents a novel method for predicting the electromagnetic field radiated by an equipment under test (EUT) in free space. The method is based on the knowledge of the electric field values close to the metallic walls of a reverberation chamber where the device is placed. From these field samples, a set of equivalent sources is retrieved. The equivalent sources likewise produce in free space the same field radiated by the EUT.

Backscattering Analysis of Cylinder Shaped Scatterer in Vegetation Medium: Comparison Between Theories

This paper analyses the backscattering cross section of a cylinder both using traditional method model and a new numerical solution model, namely Relaxed Hierarchical Equivalent Source Algorithm (RHESA). The purpose of this study is to investigate the prospect of incorporating numerical solution model into volume scattering calculation, to be applied into microwave remote sensing in vegetation area. Results show a good match, suggesting that RHESA may be suitable to be used to model the more complex nature of vegetation medium.

Comparison of dynamic models for a DC railway electrical network including an AC/DC bi-directional power station

To face environmental issues, SNCF, the French railway, has chosen to improve the energy efficiency of its electrical power system by investigating solutions for regenerative braking. With the contribution of Railenium, a research and test center in railway activities, they aim to recover the braking energy by setting up a reversible inverter in the DC substation ”Masséna”. The issue is to test, implement and compare various control solutions to increase the energy efficiency with minimum impacts on the railway operation. In this paper, a simulation model for studying a reversible power substation is addressed by considering AC and DC equivalent electrical sources. The proposed model provides a reliable tool for analyzing the behavior of the railway electrical network during specially braking mode. In order to validate this model, its simulation results are compared with the ones obtained from Esmeralda, the SNCF professional software. A first configuration is led without the inverter and gives certified Esmeralda results and validates the proposed model despite some gaps in powers and voltages due to differences in input data and models. A second comparison with inverter is presented to highlight the main difference between the proposed model and Esmeralda. In addition, laboratory experimental activities are put forward to investigate the proposed model by using power-hardware-in-the-loop simulations. Finally, a simulation test under MATLAB software with fifty train’s traffic is presented to estimate the energy saving thanks to the installed inverter. For this latter case study, the system sent back to the national AC grid around 6.9% of the total energy consumed by all trains.

Improving the crosscorrelation method to estimate the total magnetization direction vector of isolated sources: A space-domain approach for unstable inclination values

Knowledge of the total magnetization direction of geologic sources is valuable for interpretation of magnetic anomalies. Although the magnetization direction of causative sources is assumed to be induced by the ambient magnetic field, the presence of remanence should not be neglected. An existing method of correlating total and vertical gradients of the reduced-to-the-pole (RTP) anomaly estimates the total magnetization direction well. However, due to the numerical instability of RTP transformation in the Fourier domain, an assumption should be considered for dealing with inclination values at approximately 0°. We have adopted an extension to the standard crosscorrelation method for estimating the total magnetization direction vector, computing the RTP anomaly by means of the classic equivalent layer technique for low inclination values. Additionally, an ideal number of equivalent sources within the layer is considered for reducing the computational demands. To investigate the relevant aspects of the adopted method, two simple synthetic scenarios are presented. First, a magnetic anomaly produced by a homogeneous and isolated vertical dike is considered. This test illustrates the good performance of the adopted approach, finding the true magnetization direction, even for low inclination values. In the second synthetic test, a long-wavelength component is added to the previous magnetic total-field anomaly. In this case, the method adopted here fails to estimate a reliable magnetization direction vector, showing weak performance for strong interfering magnetic anomalies. On the real data example, the application tests an isolated total-field anomaly of the Carajás Mineral Province, in northern Brazil, where the inclination of the ambient magnetic field is close to zero. The obtained results indicate weak remanence in the estimated total magnetization direction vector, which would never be reached in the standard formulation of the crosscorrelation technique.

Adjustable Coupled Optoelectronic Oscillator Based on Double Frequency Output

At present, the research and development of high-speed communication technology and the more detailed division of communication frequency band have become the hot spots all over the world, which also puts forward a greater technical challenge to the down-conversion system in the receiver. However, the key to the signal receiving performance of down-conversion system is the local vibration performance. Low phase noise, tunable wideband and strong anti-electromagnetic interference have become the new directions for the future research on oscillator. Compared with the traditional microwave local oscillator, the technical advantage of the optoelectronic oscillator is more obvious, and more research and development space is left for the development of the new frequency band of communication technology in the future. The tunable coupling optoelectronic oscillator based on the double frequency output designed in this paper uses the equivalent light source of the ring path to replace the laser, and the wavelength interval of the output spectrum is changed by adjusting the length difference of the optical fiber cavity of the ring path filter. At the same time, by adjusting the bias voltage of the double-output intensity modulator, the oscillator suppresses the fundamental frequency signal and achieves the output of the two-frequency signal. After the test, it can be known that when the optical carrier wavelength of the oscillator is 1551 nm, the tuning range of the output fundamental frequency is 1.8–9 GHZ; The output range of double frequency is 3.6–18 GHz, the output power is greater than 10 dBm, and the phase noise changes slightly at different output frequencies, which is about –102 dBc/Hz.

Animal Subjects: Literature, Zoology, and British Modernism, by Caroline Hovanec

Animal Subjects: Literature, Zoology, and British Modernism, by Caroline Hovanec

A Short Survey on Green’s Function for Acoustic Problems

Green’s functions for acoustic problems is the fundamental solution to the inhomogeneous Helmholtz equation for a point source, which satisfies specific boundary conditions. It is very significant for the integral equation and also serves as the impulse response of an acoustic wave equation. They are important for acoustic problems that involve the propagation of sound from the source point to the observer position. Once the Green’s function, which satisfies the necessary boundary conditions, is obtained, the sound pressure at any point away from the source can be easily calculated by the integral equation. The major problem faced by researchers is in the process of constructing these Green’s functions which satisfy a specific boundary condition. The aim of this work is to review some of these fundamental solutions available in the literature for different boundary conditions for the ease of analyzing acoustics problems. The review covers the free-space Green’s functions for stationary source and rotational source, for both when the observer and the acoustic medium are at rest and when the medium is in uniform flow. The half-space Green’s functions are also summarized for both stationary acoustic source and moving acoustic source, derived using the image source method, equivalent source method and complex equivalent method in both time domain and frequency domain. Each of these methods used depends on the different impedance boundary conditions for which the Green’s function will satisfy. Finally, enclosed spaced Green’s functions for both rectangular duct and cylindrical duct for an infinite and finite duct is also covered in the review.